Effective cleaning compositions and cleaning methods for use in connection with certain metal parts, and in particular with metal parts used in high stress and/or high criticality applications are frequently difficult to identify. For example, certain critical metal components used in the engines of an aircraft are formed from titanium or alloys comprising titanium. Such parts are not only typically subject to high levels of stress and/or strain, they are also critical components in the sense of having a potentially direct impact on the safety and/or reliability of the aircraft. Other metals and metal alloys, including those described hereinafter, are frequently used in similar situations and are also difficult to effectively and safely clean.
With respect to the safety of the cleaning composition and the cleaning method, one of the concerns that is relevant to the identification of such compositions and methods is the possibility of causing an unacceptable change in one or more of the important properties of the metal. For example, cleaning compositions and methods which are used to remove soils from titanium parts used in aircraft, and in particular in aircraft jet engines, must not undergo any substantial increase in embrittlement as a result of being exposed to the cleaning composition or the cleaning methods. Heretofor it has been generally accepted that halogenated solvents should not be used to remove soil from such metal parts because of the unacceptable tendency of the heretofore used halogenated compounds to cause an increase in the brittleness of the titanium. Because of the critical applications of these metal parts, even a relatively small increase in the brittleness of the metal is unacceptable.
Accordingly, applicants have come to recognize a need for new cleaning solvents and cleaning methods that are effective to remove residue from certain parts formed from metals and metal alloys without negatively affecting one or more of the important properties the metal, including in particular, without negatively affecting the brittleness of the metal.